Methods and apparatus for canceling co-channel interference in a receiving system using spatio-temporal whitening

ABSTRACT

Methods and apparatus for canceling co-channel interference in a receiving system using spatio-temporal whitening. In some embodiments, a spatio-temporal interference canceling method, and apparatus for carrying out the method are provided which effectively cancel co-channel interference despite frequency offset between the desired signal and the interferer in a TDMA type system. Real and imaginary component values of the total received signal are used for virtual diversity branches, and a vector-valued auto regressive model is used to characterize the interference. In other embodiments, spatio-temporal interference whitening is used to improve timing estimates used for synchronization. The two uses of spatio-temporal whitening can be combined in one receiver. The invention is typically implemented in one or more programmed digital signal processors or application specific integrated circuits (ASICS), embodied in a receiving system.

BACKGROUND OF THE INVENTION

A receiver that needs to demodulate a desired signal in a communicationsystem must always deal with extracting the desired signal from noise.At one time, so-called “white noise” presented the greatest concern.White noise is characterized in that the noise “signal” is random, oruncorrelated, in time and space, meaning that the amplitude, phase, andother measurable characteristics of the noise at any one time or placecannot be used to predict the characteristics at any other time andplace. Methods of designing a receiver to deal with white noise arewell-known and have been in existence for decades.

Modern communication systems, such as wireless time domain multiplexedaccess (TDMA) systems increasingly have to deal with so-called “colorednoise” which is correlated and has predictable characteristics.Co-channel interference is one example of colored noise. Co-channelinterference has become a significant problem as the population densityof people using wireless, cellular communication devices increases.Because of the traffic demand, it is necessary to re-use channels morefrequently on a geographic basis. Co-channel interference can causeproblems in different sections of a TDMA receiver. Such interference cancause difficulty with the timing estimation used for synchronization inthe initial stage of processing a received signal. It can also createerrors filtering and demodulating the signal in subsequent stages.

FIG. 1 illustrates the received signal at wireless terminal 101 wherethere is both co-channel interference and white noise present. Basestation 102 is transmitting a desired signal over a channel designatedC_(d) and base station 103 is transmitting an interfering signal or“interferer” over a channel designated C_(i). Other interference issimply referred to as “noise” n. Given that each channel has specificcharacteristics that are represented with complex valued quantities, thetotal received signal at wireless terminal 101 can be represented as:r=C _(d) {circle around (x)}S _(d) +C _(i) {circle around (X)}S _(i) +n,where S_(d) is the desired signal and S_(i) is the interferer. Note thatr is complex valued even where the signals, S_(d) and S_(i) arereal-valued. FIG. 2 illustrates the spectrums of the desired signal andthe interferer, 201 and 202 respectively, in the frequency domain.

One known way to deal with co-channel and other colored interference incommunication systems is to use some type of whitening filter to“whiten” the interference, so that the desired signal now only needs tobe distinguished from white noise. Temporal whitening involves removingtemporal correlation from the interfering signal and requires knowledgeof the interfering signal's characteristics at different points in time.Spatial whitening involves removing spatial correlation from theinterfering signal and requires knowledge of the interfering signal'scharacteristics at different points in space. True, spatial whitening inwireless systems requires multiple antennas. A signal is said to have adifferent “diversity branch” for each antenna. The two types ofwhitening can be combined, resulting in whitening in both time andspace, commonly called “spatio-temporal” whitening. With any kind ofwhitening, knowledge of the characteristics of the channel is alsoneeded to extract and demodulate the desired signal from the whitenedsignal.

In TDMA systems, such as those that implement the well-known GlobalSystem for Mobile (GSM), General Packet Radio Service (GPRS), andEnhanced General Packet Radio Service (EGPRS) standards and theirvarious incarnations, a signal is received as a stream of timeslots.Each timeslot contains a known training sequence, also called a “syncword.” FIG. 3 illustrates such a timeslot, with training sequence, 301.Since the contents of the training sequence is known, thecharacteristics of the desired and interfering signals can be isolatedin time and space, and used for spatio-temporal whitening just prior todemodulating the desired signal, using multiple antennas to perform thespatio-temporal whitening. Co-channel interference is also a problem formobile terminals. However, since only one antenna is available, spatialor spatio-temporal whitening is difficult. Additionally, spatio-temporalwhitening just prior to demodulating does not increase synchronizationaccuracy in the presence of co-channel interference.

BRIEF SUMMARY OF THE INVENTION

In some embodiments of the invention, interference in a received signalis cancelled prior to demodulation by determining spatio-temporal,time-varying whitening filter parameters and time-varying channelparameters based on a frequency offset between an interferer and adesired signal. One way to determine the time-varying parameters is todetermine fixed parameters first and then rotate them using thefrequency offset. The filter parameters are applied to the receivedsignal to obtain a whitened signal. The whitened signal is thendemodulated using the time-varying channel parameters. Co-channelinterference is effectively canceled despite any frequency offsetbetween the interferer and the desired signal. Prefiltering is providedusing the time-varying channel parameters if needed. Time-varyingwhitening filter and channel parameters can also be determined bysampling portions of timeslots in the received signal and updating theparameters for each selected portion. In this case, co-channelinterference is effectively canceled despite any frequency offset orslot misalignment between the interferer and the desired signal.

In another embodiment, the entire received signal is de-rotated usingthe frequency offset between the desired signal and the interferer.Time-invariant whitening filter parameters and initial channelparameters are determined, in TDMA systems, using the training sequenceof the timeslot of interest. The time-invariant whitening filterparameters are used to whiten the received signal over the timeslotprior to demodulation to produce the whitened signal. Time-varyingchannel parameters for demodulation and prefiltering are obtained byrotating the initial channel parameters with the frequency offset.

In other embodiments, synchronization is improved by includingspatio-temporal whitening in the timing estimation process in theinterference whitening synchronization block or synchronization andinitial channel estimation block of a receiver. In this case a pluralityof signal samples is produced for a portion of the received signal,typically, the training sequence. They may be produced either bydecimating to reduce the number of samples per symbol, or they may beproduced by first applying a timing estimation method withoutspatio-temporal whitening. In any case, spatio-temporal interferencewhitening is applied to each of the plurality of signal samples toproduce a plurality of whitened signal samples. The best sample isdetermined from the whitened signal samples based on channel estimatesand on a relative, minimum value of a specified metric. The receiver issynchronized based on this best sample. The synchronization withspatio-temporal whitening may be applied to all signals receiver, or itmay be selectively applied only when needed, depending on thechannel-to-noise ratio achieved with a more traditional, lesscomputationally intensive method.

Apparatus to carry out the invention is typically implemented in one ormore programmed digital signal processors or application specificintegrated circuits (ASICS). The apparatus that carries out theinvention may include synchronization logic using spatio temporalinterference whitening (STIW). The synchronization logic may include adecimator and a selection system to determine the best sample to use forsynchronization from a plurality of samples. The apparatus also mayinclude a single antenna interference rejection (SAIR) block thatdetermines the channel parameters and filter parameters. These blocksmay be combined. In one embodiment, the SAIR block applies the whiteningfilter to the received signal based on a frequency offset between thedesired signal and an interferer. Demodulation logic demodulates thewhitened signal using the channel parameters. The demodulation logic insome embodiments includes either decision feedback sequence estimation(DFSE) or maximum likelihood sequence estimation (MLSE). Prefilteringmay also be provided.

The invention can be embodied in any receiving system, including, butnot limited to: a wireless terminal having a single antenna; a basestation with a single antenna; or processing circuitry that deals withthe signal at a single antenna in a larger system using multipleantennas, whether a base station, mobile terminal or other receivingsystem. In the case of a TDMA based mobile terminal, the invention canbe embodied in baseband logic that is operatively connected to a radioblock and a main processor system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a network block diagram that illustrates an operatingenvironment in which co-channel interference is present.

FIG. 2 is a frequency domain graph illustrating co-channel interference.

FIG. 3 illustrates a known TDMA timeslot having a training sequence,otherwise known as a sync word.

FIG. 4 is a high-level block diagram of a receiving system according tosome embodiments of the invention.

FIG. 5 is another high-level block diagram of a receiving systemaccording to other embodiments of the invention.

FIG. 6 is a flowchart illustrating the interference rejection methodaccording to one embodiment of the invention.

FIG. 7 is a block diagram of a single-antenna interference rejection(SAIR) block used in a receiving system according to an embodiment ofthe invention.

FIG. 8 is another flowchart illustrating the interference rejectionmethod according to an embodiment of the invention.

FIG. 9 is another block diagram of a single-antenna interferencerejection (SAIR) block used in a receiving system according to anembodiment of the invention.

FIG. 10 is another flowchart illustrating the interference rejectionmethod according to an embodiment of the invention.

FIG. 11 illustrates slot misalignment as handled during interferencecanceling according to one embodiment of the invention.

FIG. 12 is another flowchart illustrating the interference rejectionmethod according to an embodiment of the invention.

FIG. 13 is another block diagram of a receiving system according to anembodiment of the invention.

FIG. 14 is another block diagram of a single-antenna interferencerejection (SAIR) block used in a receiving system according to anembodiment of the invention.

FIG. 15 illustrates the general concept of sampling a portion of areceived signal to estimate timing for course synchronization.

FIG. 16 is a block diagram showing a interference whiteningsynchronization block for a receiving system according to an embodimentof the invention.

FIG. 17 is another block diagram showing another interference whiteningsynchronization block for a receiving system according to an embodimentof the invention.

FIG. 18 is a flowchart illustrating the process of timing estimationaccording to an embodiment of the invention.

FIG. 19 is another flowchart illustrating the process of timingestimation according to another embodiment of the invention.

FIG. 20 is a block diagram of a receiving system illustrating certainaspects of a timing estimation method according to an embodiment of theinvention.

FIG. 21 is a block diagram of a receiving system illustrating certainaspects of a timing estimation method according to another embodiment ofthe invention.

FIG. 22 is a block diagram of a wireless terminal which can embody theinvention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is typically embodied in a receiving system for acommunication network employing time domain multiplexed access (TDMA).The embodiments disclosed are not restricted to any particular standard,however. As previously mentioned, the well-known Global System forMobile (GSM) communication system is one example of a TDMA system whichmight employ the invention. The timeslot illustrations shown herein arebased on GSM. However, differences in these timeslot arrangements, suchas including the training sequence in some other part of the timeslot,will not affect the operation of the invention.

It should also be understood that not every feature of the receivingsystem described is necessary to implement the invention as claimed inany particular one of the appended claims. Various elements of receiversare described to fully enable the invention. It should also beunderstood that throughout this disclosure, where a process or method isshown or described, the steps of the method may be performed in anyorder or simultaneously, unless it is clear from the context that onestep depends on another being performed first.

Some of the block diagrams and flowcharts, which are used to illustratethe inventive concepts, are not mutually exclusive. Rather, each one hasbeen tailored to illustrate a specific concept discussed. In some cases,the elements or steps shown in a particular drawing co-exist with othersshown in a different drawing, but only certain elements or steps areshown for clarity. For example, the synchronization methods usingspatio-temporal whitening can be used independently in the samereceiving system with another independent single-antenna interferencewhitening (SAIR) block just prior to demodulation and/or prefiltering.

The invention includes the application of improved uses ofspatio-temporal whitening in at least two places in a TDMA typereceiving system. FIGS. 4 and 5 present high-level block diagramsillustrating these uses. FIG. 4 illustrates a receiving system includinga first stage, 401, which is a synchronization and channel estimationlogic block according to the prior art. SAIR 402 is a single-antennainterference rejection block, according to the invention, which offersimproved performance in the presence of co-channel interferer whichexhibits a frequency offset as compared to the desired signal. Thesystem of FIG. 4 also includes a prefilter 403 and a decision feedbacksequence estimation (DFSE) block, 404. The DFSE performs demodulationusing estimated channel parameters. These elements receive a receivedsignal and produce soft values for the received symbols to be furtherprocessed by parts of the receiving system which are known to those ofordinary skill in the art and which are omitted for clarity.

FIG. 5 illustrates embodiments where spatio-temporal whitening isincluded in the synchronization and channel estimation logic accordingto the invention. Joint synchronization and spatio-temporal interferencewhitening (STIW) block 500 is also referred to herein as an“interference whitening synchronization block” to distinguish it fromthe synchronization and channel estimation logic of the prior art shownin FIG. 4. Prefilter 503 and DFSE block 504 are essentially the same asshown in FIG. 4. It should be noted that the interference whiteningsynchronization block, or joint synchronization and STIW block, 500, asshown in FIG. 5 can make use of any kind of spatio-temporal interferencewhitening (STIW) filter. The SAIR discussed throughout this disclosureis one particular type of STIW. The interference whiteningsynchronization block of the invention can use SAIR, and in effect,combine the functions of the SAIR block in FIG. 4 with the functions ofthe joint synchronization and STIW block of FIG. 5. It is also possibleto have two SAIR functions, one in block 500 of FIG. 5, and a separateone placed as shown in FIG. 4. However for synchronization withinterference whitening according to the invention, any kind of STIW willdo.

A brief overview of the concept of separating a signal into virtualdiversity branches based on real and imaginary parts follows. The SingleAntenna Interference Rejection (SAIR) algorithm is an algorithm thatenables interference rejection with only one antenna. The algorithmconcentrates on real-valued modulation schemes, such as binary phaseshift keying (BPSK) and Gaussian minimum shift keying (GMSK). Such analgorithm can be implemented as an equalizer based on maximum likelihoodsequence estimation (MLSE), or on decision feedback sequence estimation(DFSE). The main difference between MLSE and DFSE is that DFSE requiresa prefilter which must be taken into account in the whitening filtermatrix. The real and imaginary parts of the signal are referred to asthe I and Q channels, respectively. Additionally, a SAIR algorithmmodels the noise and interference as a vector-valued auto regressive(VAR) process in order to design a finite impulse response (FIR) matrixwhitening filter.

A better model of the complex signal r previously discussed isrepresented by the equation:

${{\overset{\sim}{r}(n)} = {{\sum\limits_{m = 0}^{L}{{\overset{\sim}{h}(m)}{s\left( {n - m} \right)}}} + {\overset{\sim}{v}(n)}}},$where {tilde over (h)}(m) is the complex-valued channel impulse responseof length L+1, s(n) is sent symbols and {tilde over (v)}(n) denotes theadditive noise and interference. Splitting the above equation into realand imaginary parts to separate the I and Q channels yields:

${r(n)} = {\left\lbrack \frac{r_{I}(n)}{r_{Q}(n)} \right\rbrack = {{\underset{m = 0}{\overset{L}{\sum\;}}{\left\lbrack \frac{h_{I}(m)}{h_{Q}(m)} \right\rbrack{s\left( {n - m} \right)}}} + {{v(n)}.}}}$Note that since s(n) is real-valued, it can be estimated from both thereal and imaginary parts of the received signal.

The noise and interference is modeled as a VAR process by the followingequation:

${{v(n)} = {\left\lbrack \frac{v_{I}(n)}{v_{Q}(n)} \right\rbrack = {{\sum\limits_{k = 1}^{K}{A_{k}\left\lbrack \frac{v_{I}\left( {n - k} \right)}{v_{Q}\left( {n - k} \right)} \right\rbrack}} + {e(n)}}}},$where A_(k) is the matrix of VAR coefficients,

${A_{k} = \begin{bmatrix}{a_{11}(k)} & {a_{12}(k)} \\{a_{21}(k)} & {a_{22}(k)}\end{bmatrix}},{1 \leq k \leq K},$and where the noise vector,

${{e(n)} = \left\lbrack \frac{e_{I}(n)}{e_{Q}(n)} \right\rbrack},$is assumed to be white and Gaussian.

Given the above, a matrix FIR whitening filter with coefficients W_(k)can be designed as:

$W_{k} = \left\{ {\begin{matrix}A_{k} & {{{for}\mspace{14mu} k} > 1} \\I & {{{for}\mspace{14mu} k} = 0}\end{matrix}.} \right.$The whitened signal then becomes:

${r_{w}(n)} = {{\sum\limits_{k = 0}^{K}{W_{k}{\sum\limits_{m = 0}^{L}{\left\lbrack \frac{h_{I}(m)}{h_{Q}(m)} \right\rbrack{s\left( {n - m - k} \right)}}}}} + {\sum\limits_{k = 0}^{K}{W_{k}{{v\left( {n - k} \right)}.}}}}$Applying the VAR equation yields:

${{r_{w}(n)} = {{\sum\limits_{i = 0}^{L + K}{\left\lbrack \frac{b_{I}(i)}{b_{Q}(i)} \right\rbrack{s\left( {n - i} \right)}}} + {e(n)}}},$where b(i) denotes the channel after whitening. The noise is nowtemporally white and uncorrelated.

In order to obtain uncorrelated elements of the noise e(n), I/Q noisedecorrelation is performed according to:{overscore (r)} _(w)(n)=Dr _(w)(n),where D is a matrix with the property,Q ⁻¹ =D ^(T) D.The matrix D is calculated using a Cholesky factorization scheme,ultimately resulting in:

${{{\overset{\_}{r}}_{w}(n)} = {{\sum\limits_{i = 0}^{K + L}{\left\lbrack \frac{{\overset{\_}{b}}_{I}(i)}{{\overset{\_}{b}}_{Q}(i)} \right\rbrack{s\left( {n - i} \right)}}} + {\overset{\_}{e}(n)}}},$where ē(n) is a white zero mean noise vector with mutually uncorrelatedelements and where {overscore (b)}(i) is the channel impulse responseafter whitening and I/Q noise decorrelation. In practical application,the VAR matrix A_(k), the covariance matrix Q, and b(i) can be estimatedusing an indirect, generalized least squares method.

In the above discussion, it is assumed that the interferer does not haveany frequency offset or timeslot misalignment as compared to the desiredsignal. In this case, the whitening filter parameters are obtained overthe synch word of a timeslot and applied to the received signal for thewhole timeslot. If there is frequency offset in the interfering signal,the optimal whitening filter parameters will change over time, as theinterfering signal will be rotated depending on the amount of thefrequency error. Therefore, if the parameters that are obtained for thewhitening filter over the synch word as shown above are applied to thewhole received signal, the frequency offset may reduce some of theperformance gain that could otherwise be obtained. Slot misalignmentbetween the interfering signal's timeslots and the desired signal'stimeslot can have a similar effect.

There are several ways the SAIR can be improved to take into account thefrequency offset of a co-channel, interfering signal. If the frequencyoffset of the interferer is known, time-varying whitening filterparameters including the matrix coefficients can be obtained.Time-varying channel parameters can also be obtained. These time-varyingparameters can be obtained directly. Alternatively, the initialwhitening filter coefficients and channel coefficients can be obtainedas described above, discounting frequency offset, and then thecoefficients can be updated by rotating them using the knowledge of thefrequency offset. Coefficients are up-dated in each direction from thesync word as follows:a′ ₁₁(n)=a ₁₁ cos²(2πf ₀ n)+a ₂₂ sin²(2πf ₀ n−(a ₁₂ +a ₂₁)cos(2πf ₀n)sin(2πf ₀ n)a′ ₁₂(n)=a ₁₂ cos²(2πf ₀ n)+d ₂₁ sin²(2πf ₀ n−(a ₁₁ +a ₂₂)cos(2πf ₀n)sin(2πf ₀ n)a′ ₂₁(n)=a ₂₁ cos²(2πf ₀ n)+d ₁₂ sin²(2πf ₀ n) −(a ₁₁ +a ₂₂)cos(2πf ₀n)sin(2πf ₀ n)a′ ₂₂(n)=a ₂₂ cos²(2πf ₀ n)+a ₁₁ sin²(2πf ₀ n) −(a ₁₂ +a ₂₁)cos(2πf ₀n)sin(2πf ₀ n)where a_(ij) is the (ixj)th element of the whitening filter parametermatrix A.

The original channel parameters that were obtained only over the syncword can be updated as:b(n)=[Γ·Ψ(n)]·D′(n),where, for a second order VAR process,

$\Gamma = {{\begin{bmatrix}h_{1}^{T} & 0 & 0 \\h_{1}^{T} & h_{2}^{T} & 0 \\h_{1}^{T} & h_{2}^{T} & h_{3}^{T} \\\vdots & \vdots & \vdots \\h_{L - 2}^{T} & h_{L - 1}^{T} & h_{L}^{T} \\0 & h_{L - 1}^{T} & h_{L}^{T} \\0 & 0 & h_{L}^{T}\end{bmatrix}\mspace{25mu}{\Psi(n)}} = {\begin{bmatrix}{A_{0}^{\prime}(n)} \\{A_{1}^{\prime}(n)} \\{A_{2}^{\prime}(n)}\end{bmatrix}.}}$The prefilter coefficients are calculated based on the initial channelestimates over the sync word and can be fixed over the whole timeslot.Note that the whitening filter parameters do not change considerably foreach consecutive sample for more reasonable amounts of frequency offset(in the range of 200–500 Hz). Therefore, updating the parameters mightnot be necessary at each sampling point in every situation. It may besufficient to divide the timeslot into segments and update theparameters on a segment-by-segment basis, thus reducing thecomputational complexity. How often such an update is needed depends onthe amount of the frequency offset.

FIG. 6 is a high-level flowchart of these embodiments of the invention.At step 601, time-varying whitening and channel parameters areestimated, typically based on the training sequence, taking into accounta known-frequency offset. At step 602, the time varying whitening filterparameters are applied to the whole time-slot. At step 603, the timeslotis demodulated using the time varying channel parameters.

FIG. 7 is a block diagram of the SAIR block according to the presentembodiment. Initial channel and whitening filter parameters areestimated at 701 based on the training sequence in a sampled, receivedsignal. These parameters are then rotated by rotation block 702 usingthe frequency offset of the interferer. Spatio-temporal whitening usingthe time-varying parameters resulting from the rotation is applied bythe whitening filter, 703, and a whitened signal is produced.Time-varying channel parameters are also produced and passed along tothe prefilter and demodulation logic of the receiver system.

FIG. 8 illustrates the process carried out by the apparatus of FIG. 7 inanother flowchart. At step 801 the initial whitening and channelparameters are determined. At step 802 these parameters are rotated toobtain time-varying parameters. At step 803 they are applied via thefilter to whiten the entire received timeslot. At step 804 the timeslotis demodulated using the time varying channel parameters.

Another way to account for frequency offset in the SAIR is to de-rotatethe received signal based on the frequency offset. The received signalwith a frequency offset in the interferer is given by:

${\overset{\_}{r}(n)} = {{\sum\limits_{m = 0}^{L}{{\overset{\_}{h}(m)}{s\left( {n - m} \right)}}} + {{\overset{\_}{v}(n)}{{\mathbb{e}}^{j\; 2\pi\; f_{0}n}.}}}$The de-rotated signal can be written as:

${{{\overset{\_}{r}}^{\prime}(n)} = {{{\overset{\_}{r}(n)}{\mathbb{e}}^{{- 2}\pi\; f_{0}n}} = {{{\mathbb{e}}^{{- 2}\pi\; f_{0}n}{\sum\limits_{m = 0}^{L}{{\overset{\_}{h}(m)}{s\left( {n - m} \right)}}}} + {\overset{\_}{v}(n)}}}},$which becomes,

${r^{\prime}(n)} = {{{C(n)}{\sum\limits_{m = 0}^{L}{{h(m)}{s\left( {n - m} \right)}}}} + {{v(n)}.}}$

Now, the interferer does not have a frequency offset, but the desiredsignal has a frequency offset. The channel taps for the desired signalcan be rotated in time accordingly. The SAIR algorithm can be usedwithout accounting for the frequency offset for the whitening filterparameters. Time-varying channel parameters will still have to beobtained as before. Applying the whitening filter in this case resultsin:

${r_{w}^{\prime}(n)} = {{D\left\lbrack {\sum\limits_{k = 0}^{K}{W_{k}{C^{H}\left( {n - k} \right)}{\sum\limits_{m = 0}^{L}{{h(m)}{s\left( {n - m - k} \right)}}}}} \right\rbrack} + {{{De}(n)}.}}$

FIG. 9 illustrates an embodiment of the invention where the frequencyoffset is accounted for by de-rotating the received signal. De-rotationis accomplished at block 901 based on the frequency offset of theinterferer, before application of the SAIR. Thus, the frequency offsetof the interferer is eliminated. Therefore, the interferer istime-invariant, however, the desired signal is time-varying. Whiteningfilter parameters and channel parameters are estimated using thetraining sequence at block 902. Since the interferer does not change,constant whitening filter parameters that are obtained over the trainingare applied to the whole received slot by spatio-temporal whiteningfilter 903. However, the channel estimates of the desired signal arerotated according to the original frequency offset of the interferer.Therefore, according to this embodiment, the whitening filter parametersare constant over the whole slot, but the desired signal's channelparameters will be time-varying. Both the fixed whitening filterparameters and fixed channel parameters can be obtained over thetraining. The channel parameters are then rotated accordingly to obtainthe correct time varying channel parameters.

FIG. 10 illustrates the process just discussed in flowchart form. Atstep 1001 the received signal is de-rotated. At step 1002,time-invariant whitening filter parameters are obtained. Channelparameters are also obtained over the training sequence. At step 1003,time-invariant whitening filter parameters are applied to the entiretimeslot. At step 1004 the channel parameters are rotated. At step 1005the estimated channel parameters are used to demodulate the timeslot.

Another alternative for providing the SAIR function in the presence of afrequency offset can be used if the frequency offset is unknown and noteasy to estimate. In this embodiment, the whitening filter parametersare tracked over the data portion of the timeslot. Tracking can be donecontinuously or on a portion-by-portion basis. For the tracking,estimated data is initially used. The prefilter parameters arecalculated over the synch word and applied to the received signal. Withsuch tracking, slot-misaligned cases can also be handled. When theimpairment characteristics change, parameters can be updated. FIG. 11illustrates a slot-misaligned situation. As can be seen, interferer slot1101 is delayed relative to desired signal slot 1102. FIG. 12illustrates the method just described in flowchart form. To accomplishthe tracking, a SAIR with fixed parameters is applied over the synchword to calculate the initial whitening filter parameters and channelparameters, as shown at step 1201. At 1202 the first portion of thetimeslot is set to the “new portion”. At 1203, the whitening filterusing the initial parameters is applied. At 1204, the new portion isdemodulated using the channel parameters. Prefiltering is also appliedif needed. At 1205 a test is made to determine if the demodulation ofthe timeslot is complete. If so, the process stops. If not, whiteningfilter and channel parameters for the next portion, if there is one, areestimated from the current portion at 1206. The next “new portion” isretrieved at 1207.

FIG 13 shows a block diagram of the pertinent parts of a receivingsystem implementing the embodiment discussed with respect to FIG. 12.Synchronization and channel estimation logic 1301 are present as before.SAIR block 1302 obtains the whitening filter parameters and desiredsignal's channel parameters over the training sequence, which are outputat 1303. The whitening parameters are applied to a portion of the slotjust after the synch word, then this portion of the slot is demodulatedthrough prefilter 1304 and DFSE block 1305 using the whitened samplesand the channel parameters of the desired signal. The demodulatedsymbols over this portion of the slot are used to estimate new whiteningfilter and channel parameters. The new whitening parameters are appliedto each new portion of the timeslot by SAIR block 1306 to obtain thewhitened samples for this portion and the process continues likewise.SAIR block 1302 and SAIR block 1306, though logically separate, may bein fact implemented by the same SAIR logic.

FIG. 14 shows a more detailed block diagram of SAIR block 1306 of FIG.13. Since the signal is being supplied to the SAIR block and aportion-by-portion basis, there is no channel or signal rotation. ThisSAIR block is similar to a SAIR block that might be used in a systemthat does not take frequency offset into account, except that thewhitening filter and channel estimation block 1401 operates on each newblock, not just on the training sequence. Spatio-temporal whiteningfilter 1402 is applied using the estimated filter parameters to producea whitened signal.

Other embodiments are now described in which STIW is applied to thetiming estimation performed in the synchronization logic of a receiver.The application of spatio-temporal interference whitening at this stagecan increase channel-to-noise ratio by determining the best timingoffset with which to receive the symbols being sent in a timeslot. As iswell-known, synchronization logic in TDMA receivers performs coursesynchronization first, followed by fine synchronization. It is assumedthat course synchronization is first performed before the interferencewhitening synchronization block by a traditional method. Thesynchronization method that makes use of STIW that is described indetail here is for fine synchronization.

Fine synchronization according to the invention finds the best referencepoint (among all possible reference points determined in a coarsesynchronization) for the down-sampling and demodulation of the receivedsamples. Finding the correct reference point is very important to thesignal-to-noise-ratio (SNR) of the received signal, sometimes referredto as channel-to-noise (C/N) ratio in a TDMA system. FIG. 15 illustrateshow course synchronization is accomplished what a timeslot looks likejust before fine synchronization according to the invention. 1501illustrates the timeslot before any synchronization, showing symbols S-5through S5. 1500 shows the same timeslot after course synchronization. Acourse sampling and timing hypothesis, 1502, showing samples 1, 2, 3, .. . N, one sample per symbol, results from the course synchronization.1503 shows different potential sampling points within a symbol. Finesynchronization will need to determine which of these sampling points isbest.

Before describing these embodiments of the invention in detail, it isuseful to discuss one known, conventional way of performing finesynchronization (or timing estimation). Assume that the coarsesynchronization reduced the possible number of symbols to +/−K symbols,and assume that for each symbol there are M sampling position (forexample 8 samples per symbol). Therefore, the total number of samplinghypotheses is (2K+1)M. Further, assume that for each sampling positionhypothesis, the received signal is down-sampled to one sample persymbol, resulting in r_(k)(n) received samples for the kth samplingposition hypothesis. A least square channel estimation is performedusing the knowledge of the synch word. Using the estimated channelparameters, Ĥ_(k) and the known synch sequence, S, a replica of thereceived samples is calculated as {circumflex over (r)}_(k)(n). Thedifference between what is received and what is modeled is calculatedby:

$e_{k} = {\frac{1}{N}{\sum\limits_{n = 1}^{N}{{{r_{k}(n)} - {{\hat{r}}_{k}(n)}}}^{2}}}$where N is the length of the synch sequence. This timing offset estimateminimizes the error among all possible timing hypotheses.

According to the invention, both interference cancellation and timingoffset estimation are done jointly within the synchronization logic. Forthe interference cancellation part of the process a spatio-temporalinterference whitening (STIW) approach is employed. The STIW used in thesynchronization can be SAIR as previously described, or other types ofSTIW, including STIW using multiple antennas.

A block diagram of an interference whitening synchronization block usingSTIW is shown in FIG. 16. The logic of FIG. 16 is normally located inblock 500 of FIG. 5. This timing estimation can be independently appliedto any receiver structure, or to any equalization scheme. FIG. 16 onlyshows one of these applications. Similarly, application of STIW in thetiming offset estimation process does not necessarily require the use ofSTIW before equalization. It is possible to apply STIW only for thetiming offset estimation, and perform equalization without whitening thereceived samples. A typical receiver includes the blocks that preprocessthe received antenna signal (signal preprocessor). Typically, thepreprocessor includes receiver filtering, amplifiers, and mixers thatproduce baseband signal. The received signal shown in all of the figuresherein is the preprocessed signal.

FIG. 16 shows a block diagram of the joint timing offset estimation andinterference whitening that is sometimes referred to herein asinterference whitening synchronization. The received samples aredecimated by decimator 1601 based on sample timing from the sampletiming selector, 1602, to obtain the down-sampled received samples(usually one sample per symbol). The down-sampled received samples(around the training region) are passed through STIW block 1603. Theoutput of the STIW block is the whitened received samples z_(k)(n). Inthis embodiment, channel estimates Ĉ_(k) are passed trough the samewhitening filters. The filtered channel estimates and the known trainingsequence s(n) are used to calculate a replica of the whitened receivedsamples {circumflex over (z)}_(k)(n). This calculation is performed inmetric calculator block 1604. The difference between what is receivedand what is modeled is calculated as:

$e_{k} = {\frac{1}{N}{\sum\limits_{n = 1}^{N}{{{{z_{k}(n)} - {{\hat{z}}_{k}(n)}}}^{2}.}}}$

The calculated metric value from above is passed to the metriccomparator and minimum metric selector block, 1605. This block comparesall the calculated metric values corresponding to all the sample timingpositions and finds the minimum metric value. The minimum metric valueand the corresponding sample timing position is selected as theestimated sample timing position. The sample timing selector knows allthe possible timing hypotheses, and one-by-one, provides the timingpositions to the decimator. The sample timing selector knows whetherthere is another sample timing position to evaluate. Since the sampletiming selector, 1602, is connected to the minimum metric selector, whenall the hypotheses are evaluated, the sample timing selector providesthe timing hypotheses that has the minimum metric to the decimator,1601. The sample time selector 1602 may also be connected to the STIWblock, 1603 to indicate that this is the best timing position and stopthe process. This connection is represented by the dotted arrow in FIG.16.

Decimator 1601 decimates the oversampled signal. Starting from thedecided timing position, it selects one (or more) samples from eachsymbol. The decimator does not need to decimate the entire timeslot totest all the hypotheses. Only training samples are used. At the end ofthe process, when the best timing offset has been selected, thedecimator may decimate the whole timeslot. The STIW algorithm in block1603 may then operates on the decimated samples, calculating the vectorvalued whitening filter parameters and whitening all the receivedsamples.

FIG. 17 is a block diagram for the case where the receiver performsspatio-temporal whitening only for the timing offset estimation, anddoes not apply whiting to the whole received signal. Returning to FIGS.4 and 5, FIG. 17 would represent the case where block 500 of FIG. 5 doesnot actually combine the functions of blocks 401 and 402 of FIG. 4. Inthis case, blocks 1701, 1702, 1703, 1704 and 1705 are similar to blocks1601, 1602, 1603, 1604 and 1605 of FIG. 16. However, the STIW block anddecimator 1701 never operate on the entire timeslot. Instead, finaltiming estimation can be used to decimate the signal at decimator 1710,and the decimated signal can be provided to other parts of the receiver,1711. The other parts of the receiver may include a SAIR block as shownat 402 of FIG. 4, and discussed in previous sections of thisapplication, especially if STIW 1703 is not a SAIR implementation.

FIG. 18 illustrates the method described above in flowchart form. Atstep 1801, the minimum metric is set to some maximum acceptable value.For purposes of this example, the minimum metric has been set to1,000,000. The best sample is also designated as the “0^(th)” sample. Atstep 1802, the next sample (sample k) is retrieved. At 1803, the signalis decimated based on the timing of sample k. At step 1804, the STIWalgorithm is applied to the decimated signal. At step 1805, the metricvalue is computed for the whitened signal as decimated based on thetiming of sample k for the training sequence, also taking into accountthe channel estimates over the training sequence. At 1806, the currentmetric is compared to the minimum metric. If the current metric is notless than the minimum metric, processing branches to decision point1808, where a determination is made as to whether sample k is the lastsample. If not, the process repeats, starting with step 1802. If so, theprocess ends. If the current metric is less than the minimum metric atdecision point 1806, the minimum metric is set to the current metric andthe best sample is set to the current sample, k, at step 1807.

The peak and average computational complexities for the joint whiteningand timing estimation are higher than for a conventional timingestimation approach. The average complexity can be reduced by employingthe joint approach of the invention only if the carrier-to-noise-ratio(C/N) of the current slot is below some threshold value. If the C/Nvalue is above the threshold, a less computationally intensive approachfor timing estimation may perform well. In other embodiments of theinvention, conventional timing estimation without STIW is combined withthe interference whitening synchronization using joint timing estimationand STIW. FIG. 19 is a flowchart that illustrates one way to combine thealgorithms. A conventional timing estimation is applied first to thereceived timeslot at step 1901. The channel estimates and the residualerror (minimum metric value) are calculated using the estimated timingoffset at step 1902. The C/N value is calculated from the channelestimates and the residual error value estimate at step 1903. The energyof the combined channel taps provides C, and the residual error providesN. If the estimated C/N value is below a threshold value at decisionpoint 1905, then the joint timing estimation and STIW algorithm isemployed at step 1906. Otherwise we use the timing estimates of theconventional algorithm as shown at 1904.

FIG. 20 shows a block diagram of the combined algorithm as describedabove. A conventional timing estimation is applied first for thereceived timeslot by block 2001. Then, the channel estimates and theresidual error are calculated from the estimated timing offset. If theC/N value is below a threshold value, then timing estimation is switchedto the joint timing estimation and STIW algorithm implemented in block2002. Decisions are made by the control unit, 2003. The “other receiverparts,” 2004 are as previously described.

Another way of combining the conventional timing estimation with theinterference whitening synchronization block implementing joint timingestimation and STIW is to employ the conventional timing estimation tonarrow-down the possible timing position choices. Then, joint algorithmcan be used to obtain a finer timing estimate. FIG. 21 is a blockdiagram that also illustrates the signal flow for this embodiment.Assume that initially there are X possible timing offset positions. Theconventional algorithm is executed by block 2101 first. From theconventional algorithm, the metric values (residual errors)corresponding to all the timing positions are calculated. These metricvalues and the initial timing positions are passed through comparatorand selector block, 2102, where a group (Y out of X, where Y<X) of thesmallest metric values and the corresponding timing positions areselected. These selected timing positions are fed to the interferencewhitening synchronization block, 2103, where the joint timing estimationand STIW algorithm are executed for better tuning. Other receiver parts2104 are as previously discussed.

Other embodiments could also be devised where timing offset estimationis done only for some subset of the possible timing hypotheses. Forexample, for each symbol, a random timing offset can be selected ratherthan formally hypothesizing timing sample values for each symbol. Inthis case, the timing offset hypothesis only consists of the differentsymbol timings, not the samples within the symbols.

As previously discussed, the joint synchronization and STIW approach canbe used with either single or multiple antenna receivers. There arevarious possible extensions of the to the multiple antenna receivers. Inmultiple antenna receivers, for each antenna element, instead ofemploying a conventional timing estimation, the proposed interferencewhitening synchronization algorithm can be employed to get the timing ofthat antenna element. An independent STIW algorithm (in the I-Q domain)in each antenna element can be combined with spatial whitening acrossantenna elements. The independent STIW algorithm (in the I-Q domain) ineach antenna element can be combined with another STIW algorithm acrossthe antenna elements. Such an algorithm can be performed iteratively byfirst treating each antenna element independently, then applying STIW inthe I-Q domain to get the possible timing estimates. The number ofhypotheses can optionally be reduced. STIW is then applied acrossantennas.

FIG. 22 is a block diagram of a mobile terminal that implements theinvention. FIG. 22 illustrates a terminal with voice capability, such asa mobile telephone. This illustration is an example only, and theinvention works equally well with mobile terminals that are dedicated tocommunicating with text or other forms of data. As described above, someembodiments of the invention can also work in base stations designed tocommunicate with such a mobile terminal. As shown in FIG. 22, theterminal includes radio block 2201, a baseband logic block, 2202,control logic block 2203 and an audio interface block, 2204. Withinradio block 2201, the receive and transmit information is converted fromand to the radio frequencies (RF) of the various carrier types, andfiltering is applied, as is understood in the art. Radio block 2201includes the preprocessor previously discussed. The terminal's antennasystem, 2207, is connected to the radio block. In baseband logic block2202, basic signal processing occurs, e.g., synchronization, channelcoding, decoding and burst formatting. In this example, the basebandlogic includes the SAIR of the invention. The baseband logic block alsooptionally includes the interference whitening synchronization blockaccording to the invention. Audio interface block 2204 handles voice aswell as analog-to-digital (A/D) and D/A processing. It also receivesinput through microphone 2205, and produces output through speaker 2206.Control logic block 2203, coordinates the aforedescribed blocks and alsoplays an important role in controlling the human interface components(not shown) such as a key pad and liquid crystal display (LCD). Thefunctions of the aforedescribed transceiving blocks are directed andcontrolled by one or more microprocessors or digital signal processorssuch as main processor 2208, shown for illustrative purposes. Programcode, often in the form of microcode is stored in memory 2209 andcontrols the operation of the terminal through the processor orprocessors. The mobile terminal illustrated in FIG. 22 interfaces to asmart card identity module (SIM), 2211, through a smart card readerinterface. The interconnection between the main processor, controllogic, memory, and SIM is depicted schematically. The interface is oftenan internal bus.

A mobile terminal implementation of the invention does not have to be atraditional “cellular telephone” type of terminal, but may include acellular radiotelephone with or without a multi-line display; a personalcommunications system (PCS) terminal that may combine a cellularradiotelephone with data processing, facsimile and data communicationscapabilities; a personal data assistant (PDA) that can include aradiotelephone, pager, Internet/intranet access, Web browser, organizer;and a conventional laptop and/or palmtop computer or other appliancethat includes a radiotelephone transceiver. Mobile terminals aresometimes also referred to as “pervasive computing” devices.

Some embodiments of the invention can be implemented in base stationsystems as previously described. An exemplary BSS includes a basestation controller (BSC) and base station transceivers or basetransceiver stations (BTS), each providing service for a single cellthrough an antenna system. The antenna system can have a single antenna,or multiple antennas. Each BTS includes at least one transmitter as wellas one or more receiving systems that receive timeslots on uplinkfrequencies. One or more of these receiving systems embody theinvention.

Specific embodiments of an invention are described herein. One ofordinary skill in the networking and signal processing arts will quicklyrecognize that the invention has other applications in otherenvironments. In fact, many embodiments and implementations arepossible. In addition, the recitation “means for” is intended to evoke ameans-plus-function reading of an element in a claim, whereas, anyelements that do not specifically use the recitation “means for,” arenot intended to be read as means-plus-function elements, even if theyotherwise include the word “means.” The following claims are in no wayintended to limit the scope of the invention to the specific embodimentsdescribed.

1. A method of canceling interference over a timeslot of a receivedsignal in a time domain multiplexed access communication system, themethod comprising: using a first single antenna interference rejection(SAIR) block to determine spatio-temporal, whitening filter parametersand channel parameters; applying the first SAIR block using thewhitening filter parameters to the received signal over a selectedportion of a plurality of portions of the timeslot to obtain a whitenedsignal; demodulating the whitened signal over the portion using thechannel parameters; and if additional portions of the timeslot remainun-demodulated, applying a second SAIR block to update the whiteningfilter parameters and the channel parameters based on the selectedportion of the timeslot and repeating the applying and demodulating fora new portion of the timeslot.
 2. The method of claim 1 whereindemodulating the whitened signal further comprises: prefiltering thecurrent whitened signal using the channel parameters; and applyingdecision feedback sequence estimation.
 3. The method of claim 1 whereindemodulating the whitened signal further comprises applying maximumlikelihood sequence estimation to the whitened signal.
 4. A method ofsynchronizing a receiver with a received signal, the method comprising:decimating a portion of the received signal to produce a first group ofsamples for the portion of the received signal; selecting a plurality ofsignal samples from the first group of samples based on an initialtiming estimate made without spatio-temporal whitening to produce theplurality of signal samples for a portion of the received signal;applying spatio-temporal interference whitening to each of the pluralityof signal samples to produce a plurality of whitened signal samples;determining a best whitened signal sample from among the plurality ofwhitened signal samples based on channel estimates and on a relative,minimum value of a specified metric for each of the plurality ofwhitened signal samples; and synchronizing the receiver based on timingof the best whitened signal sample.
 5. The method of claim 4 wherein theapplying of spatio-temporal interference whitening is accomplished atleast in part through the use of time-varying channel parameters andwhitening filter parameters which take into account a frequency offsetbetween the received signal and an interfering signal.
 6. A method ofsynchronizing a receiver with a received signal, the method comprising:decimating a portion of the received signal to produce a plurality ofsignal samples; estimating a timing for the received signal based on theplurality of signal samples and on channel estimates without applyingspatio-temporal whitening to the plurality of signal samples;determining if a signal-to-noise ratio of the received signal, receivedusing the timing is below a specified threshold value; applyingspatio-temporal interference whitening to each of the plurality ofsignal samples to produce a plurality of whitened signal samples, if thesignal-to-noise ratio is below the specified threshold value;determining a best whitened signal sample from among the plurality ofwhitened signal samples bused on channel estimates and on a relative,minimum value of a specified metric for each of the plurality ofwhitened signal samples, if the signal-to-noise ratio is below thespecified threshold value; and synchronizing the receiver based ontiming of the best whitened signal sample if the signal-to-noise ratiois below the specified threshold value.
 7. The method of claim 6 whereinthe applying of spatio-temporal interference whitening is accomplishedat least in part through the use of time-varying channel parameter, andwhitening filter parameters which take into account a frequency offsetbetween the received signal and an interfering signal.
 8. Apparatus forsynchronizing a receiver with a received signal, the apparatuscomprising: means for decimating a portion of the received signal toproduce a plurality of signal samples; means for estimating a timing forthe received signal based on the plurality of signal samples and onchannel estimates without applying spatio-temporal whitening to theplurality of signal samples; means for determining if a signal-to-noiseratio of the received signal, received using the timing is below aspecified threshold value; means for applying spatio-temporalinterference whitening to each of the plurality of signal samples toproduce a plurality of whitened signal samples; means for determining abest whitened signal sample from among the plurality of whitened signalsamples based on channel estimates and on a relative, minimum value of aspecified metric for each of the plurality of whitened signal samples;and means for synchronizing the receiver based on timing of the bestwhitened signal sample.
 9. A processor-controlled receiving systemenabled to cancel interference in a received signal, the receivingsystem comprising: synchronization and channel estimation logic; a firstsingle antenna interference rejection (SAIR) block connected to thesynchronization and channel estimation logic, the SAIR block fordetermining channel parameters and applying a whitening filter to thereceived signal based on a frequency offset between a desired signal andan interferer to obtain a whitened signal; demodulation logic fordemodulating the whitened signal using the channel parameters; and asecond SAIR block connected to the demodulation logic, the second SAIRblock for updating the whitening filter parameters and the channelparameters based on each selected portion of a plurality of portions ofa timeslot in the received signal.
 10. The receiving system of claim 9wherein the demodulation logic further comprises: a decision feedbacksequence estimation (DFSE) block; and a prefilter disposed between theDFSE block and the SAIR block.
 11. The receiving system of claim 9wherein the demodulation logic further comprises a maximum likelihoodsequence estimation (MLSE) block.
 12. A processor-controlled receivingsystem comprising: demodulation logic; and a interference whiteningsynchronization block preceding the demodulation logic, the interferencewhitening synchronization block disposed to receive a received signaland further comprising: a decimator disposed to receive the receivedsignal, the decimator for producing a plurality of signal samples fromthe received signal; a timing selector operatively connected to thedecimator; a spatio-temporal interference whitening (STIW) blockconnected to the decimator, the STIW block for applying spatio-temporalinterference whitening to each of the plurality of signal samples toproduce a plurality of whitened signal samples; and a selectionsubsystem connected to the timing selector and the STIW block, theselection subsystem operable to determine a best whitened signal samplefrom among the plurality of whitened signal samples based on channelestimates and on a relative, minimum value of a specified metric and forsynchronizing the receiver with the received signal based on timing ofthe best whitened signal sample.
 13. The receiving system of claim 12wherein the interference whitening synchronization block is selectivelyenabled to receive the received signal under the control of a controlunit.
 14. The receiving system of claim 13 wherein the selectionsubsystem further comprises: a metric calculator connected to the STIWblock; and a metric comparator connected to the metric calculator andthe timing selector.
 15. The receiving system of claim 13 wherein theSTIW block is a single antenna interference rejection (SAIR) block fordetermining time-varying channel parameters and applying a whiteningfilter to the received signal based on a frequency offset between thereceived signal and an interfering signal.
 16. The receiving system ofclaim 15 wherein the selection subsystem further comprises: a metriccalculator connected to the STIW block; and a metric comparatorconnected to the metric calculator and the timing selector.
 17. Thereceiving system of claim 13 further comprising a single antennainterference rejection (SAIR) block disposed between the interferencewhitening synchronization block and the demodulation logic, the SAIRblock for determining time-varying channel parameters and applying awhitening filter to the received signal based on a frequency offsetbetween the received signal and an interfering signal.
 18. The receivingsystem of claim 17 wherein the SAIR block also serves as the STIW block.19. The receiving system of claim 17 wherein the demodulation logicfurther comprises: a decision feedback sequence estimation (DFSE) block;and a prefilter disposed between the DFSE block and the SAIR block. 20.The receiving system of claim 19 wherein the selection subsystem furthercomprises: a metric calculator connected to the STIW block; and a metriccomparator connected to the metric calculator and the timing selector.21. The receiving system of claim 17 wherein the demodulation logicfurther comprises further comprises a maximum likelihood sequenceestimation (MLSE) block.
 22. The receiving system of claim 17 whereinthe selection subsystem further comprises: a metric calculator connectedto the STIW block; and a metric comparator connected to the metriccalculator and the timing selector.
 23. The receiving system of claim 22wherein the demodulation logic further comprises further comprises amaximum likelihood sequence estimation (MLSE) block.
 24. The receivingsystem of claim 12 further comprising a single antenna interferencerejection (SAIR) block disposed between the interference whiteningsynchronization block and the demodulation logic, the SAIR block fordetermining time-varying channel parameters and applying a whiteningfilter to the received signal based on a frequency offset between thereceived signal and an interfering signal.
 25. The receiving system ofclaim 24 wherein the demodulation logic further comprises: a decisionfeedback sequence estimation (DFSE) block; and a prefilter disposedbetween the DFSE block and the SAIR block.
 26. The receiving system ofclaim 25 wherein the selection subsystem further comprises: a metriccalculator connected to the STIW block; and a metric comparatorconnected to the metric calculator and the timing selector.
 27. Thereceiving system of claim 24 wherein the selection subsystem furthercomprises: a metric calculator connected to the STIW block; and a metriccomparator connected to the metric calculator and the timing selector.28. The receiving system of claim 27 wherein the demodulation logicfurther comprises further comprises a maximum likelihood sequenceestimation (MLSE) block.
 29. The receiving system of claim 24 whereinthe demodulation logic further comprises further comprises a maximumlikelihood sequence estimation (MLSE) block.
 30. The receiving system ofclaim 24 wherein the SAIR block also serves as the STIW block.
 31. Thereceiving system of claim 12 wherein the STIW block is a single antennainterference rejection (SAIR) block for determining time-varying channelparameters and applying a whitening filter to the received signal basedon a frequency offset between the received signal and an interferingsignal.
 32. The receiving system of claim 31 wherein the selectionsubsystem further comprises: a metric calculator connected to the STIWblock; and a metric comparator connected to the metric calculator andthe timing selector.
 33. The receiving system of claim 12 wherein theselection subsystem further comprises: a metric calculator connected tothe STIW block; and a metric comparator connected to the metriccalculator end the timing selector.
 34. A processor-controlled receivingsystem comprising: demodulation logic; and a interference whiteningsynchronization block preceding the demodulation logic, the interferencewhitening synchronization block disposed to receive a received signaland further comprising: synchronization and channel estimation logic forproducing a plurality of signal samples from the received signal; acomparator and selector block connected to the synchronization andchannel limitation logic; a spatio-temporal interference whitening(STIW) block connected to the comparator and selector block, the STIWblock for applying spatio-temporal interference whitening to each of theplurality of signal samples to produce a plurality of whitened signalsamples; and a selection subsystem connected to a timing selector andthe STIW block, the selection subsystem operable to determine a bestwhitened signal sample from among the plurality of whitened signalsamples based on channel estimates and on a relative, minimum value of aspecified metric and for synchronizing the receiver with the receivedsignal based on timing of the best whitened signal sample.
 35. Thereceiving system of claim 34 wherein the STIW block is a single antennainterference rejection (SAIR) block for determining time-varying channelparameters and applying a whitening filter to the received signal basedon a frequency offset between the received signal and an interferingsignal.
 36. The receiving system of claim 34 further comprising a singleantenna interference rejection (SAIR) block disposed between theinterference whitening synchronization block and the demodulation logic,the SAIR block for determining time-varying channel parameters andapplying a whitening filter to the received signal based on a frequencyoffset between the received signal and an interfering signal.
 37. Thereceiving system of claim 36 wherein the demodulation logic furthercomprises: a decision feedback sequence estimation (DFSE) block; and aprefilter disposed between the DFSE block and the SAIR block.
 38. Thereceiving system of claim 36 wherein the demodulation logic furthercomprises further comprises a maximum likelihood sequence estimation(MLSE) block.
 39. The receiving system of claim 36 wherein the SAIRblock also serves as the STIW block.